Controlling position with bias

Bias can be best understood here as a percentage value, but rather than position the view according to its center or a corner, it is the percentage of space either side of it. So if the bias towards the top is 33%, then the margin below will be twice the size of the one below it.

Setting bias is even easier than understanding it, as once a constraint is set on any opposing sides of a view, an associated slider will appear in the Properties graphic Properties editor:

A quick glance at the generated code shows the format for this attribute as follows:

app:layout_constraintHorizontal_bias="0.33" 

The value of using bias to position screen elements lies partly in the simplistic approach, but its true value comes when it comes to developing for multiple screens. There are so many models available and they all seem to have slightly different proportions. This can make design layouts that look fantastic on all of them, very time consuming and even shapes as similar as 720 x 1280 and 768 x 1280 can produce undesirable results when tested with the same layout. The use of the bias attribute goes a long way to solving these issues, and we shall see more of this later when we take a look at layout previews and the percent library.

As if all this didn't make designing a layout easy enough, constraint layouts have two other extremely handy functions that almost automate UI design: auto-connect and inference.